Thin film transistors (TFTs) are the major driving components in existing LCD devices and active matrix organic light-emitting diode (AMOLED) devices. TFTs directly affect the performance of these devices.
Existing LCD devices are usually back-lighted display devices, and include a LCD panel and a backlight module. The principle behind a LCD panel is to fill liquid crystal molecules between a TFT array substrate and a color filter (CF) substrate, and to alter the alignment of the liquid crystal molecules by the electrical field formed between the substrates as the substrates are applied with pixel and common voltages. As such, light from the backlight module is refracted to produce images.
Ultra-thin LCD devices are currently the mainstream product, and there are already LCD panels having thickness 5.9 mm and 9 mm. To support these LCD panels, their light guide plate (LGP) also should have reduced thickness. Existing LGPs already have their thickness reduced from previous 3 mm to below 2 mm. Their material is also switched from polymethyl methacrylate (PMMA) to glasses. It is expected that, in the future, glass-LGP would have thickness lower than 1 mm. As LGPs are becoming thinner, the width of light-emitting diodes (LEDs) also has to be thinner. Previously most LEDs has thickness 2.0 mm or 1.6 mm, but these days most of them have thickness 1.4 mm or 1.0 mm. When these LEDs are inserted unto printed circuit boards (PCBs), due to the precision of the workstation, some LEDs are not aligned and some have their light emission face above the LGP, causing severe light leakage. The backlight module therefore suffers low light coupling efficiency and low power utilization. On the other hand, the number of configured LEDs is also limited due to the dimension of their lead frames. The driving power to each LED is also limited by the lead frame's light fastness and heat resistance properties.